Abstract: Soil arching, as a major medium of load transfer, is closely related to the reinforcement of anti-slide piles. Gravel soil slopes contain a large number of coarse particles, which are conducive to shear stress transmission and provide conditions for the development of soil arching. To explore the arching mechanism behind piles in gravel soil slopes, a numerical model was established using the particle flow code PFC^2D. Based on the load-displacement curve of the loading wall, the evolution process of soil arching was studied through particle displacement and contact force chains. The influence of pile width, pile spacing, particle size, and soil compaction on soil arching was then analyzed using the ultimate bearing capacity of the soil arch and the pile load distribution ratio. The results show that the evolution process of the soil arch can be divided into development, weakening, and failure stages. In different stages, the variation characteristics of soil displacement around the pile and the bearing capacity of the soil arch are inconsistent. Soil arching destruction first occurs at the arch foot and is dominated by shear failure. Macroscopically, soil arch failure is manifested by a significant imbalance in the load distribution among anti-slide piles. The ultimate bearing capacity of the soil arch and the pile load distribution ratio are positively correlated with pile width, particle size, and soil compaction, but negatively correlated with pile spacing. These results can provide theoretical guidance for the optimization design of anti-slide piles in gravel soil slopes.